The invention relates to a resistance forge welding machine, comprising at least one welding head with an electrode, at least one welding transformer for generating a welding current, which is connected to the electrode, at least one drive for moving the electrode or for producing electrode pressure on the workpiece and a controller, which is connected to the drive and to the welding transformer.
In resistance forge welding, the heat for the welding point is produced by simultaneous action of an electrical current and the force of the electrode as well as the electrical resistance of the materials to be welded in the region of the point of contact of the electrodes. The workpieces generally lie flat on each other and are welded under considerable pressure at individual points by the force of the electrode. The current and the electrode force are supplied via the electrodes.
Known resistance forge welding machines are designed as single-phase or multi-phase machines. The actuation (advancement) of the movable electrode and the application of the electrode pressure to the workpiece take place by means of pneumatic cylinders. Only in rare cases are other drives, such as for example hydraulic cylinders and mechanical adjusting means (for example camshafts), used for applying the electrode force.
In addition, industrial robots are used as carriers of movable welding tools and welding tongs and are moved according to a fixed and stored program from point to point in a series of directions along the edges to be welded of the parts to be joined. At each intended welding point, the welding tongs are made to carry out spot welding by a control pulse. Industrial robots for resistance forge welding comprise a column and an arm. Fastened at the end of the arm by means of a suitable fastening flange is the welding tool or the welding tongs. To move to a particular point of the workpiece to be welded, the welding tongs are initially moved to the coordinates X, Y, Z of the point. Since, at every point, electrodes have to be arranged in a position perpendicular to the workpiece surface, two to three further movements are necessary for the welding tongs by rotating, turning etc. As a result, the kinematics of the industrial robots must allow adjustment with 5 to 7 degrees of freedom.
These movements, carried out electromotively, hydraulically or pneumatically, are initiated by a programmed controller for each welding point.
In the case of the known resistance forge welding devices, the control means for the electrode force is separate from the means for producing the electrode travel. A highly accurate movement or positioning of the electrodes and the electrode force under open-loop or closed-loop control in dependence on the respective position would be desirable, however.